Scallop shells hold clues to changes in Antarctic climate

By Nancy Ross FlaniganNews and Information Services

Collecting pretty seashells is more than a vacation pastime for scientists from the U-M and Ohio State University, whose analyses of scallop shells are filling gaps in Antarcticas temperature record for the last century.

Unlike areas that have been inhabited for long periodswhere people have measured temperatures every day for hundreds of yearsthere are very few instrumental records of temperatures on the Antarctic continent or in its vicinity that extend back to the early 1900s, the beginning of the industrial revolution, says Kyger C. Lohmann, professor of geological sciences. As a result, researchers who want to know how the area has been affected by global warming have little to go on. Although some information can be gleaned from ice cores, it is difficult to resolve seasonal variationparticularly the magnitude of summer warmingfrom the ice and snow records, says Lohmann.

But growth bands in the shell of the Antarctic scallop, a sea animal that can live 100 years or longer, do reveal annualand even seasonalenvironmental trends, Lohmann and his co-workers found.

We can see a long-term warming trend in the Antarctic continent during the last 100 years, with a major shift occurring around the early 1950s, says Lohmann. In their analysis, Lohmann and co-workers looked at ratios of isotopes (alternate forms) of oxygen in the growth bands of the scallop shells. Changes in the isotope ratios reflect changes in the chemistry of coastal waters as glaciers melt and retreat, which is an indirect measure of the continents high temperatures.

The warmer the summers, the more glacial ice melts on the continent and runs off into the surrounding waters, Lohmann explains. Small changes in the amount of glacial meltwater dramatically affect the chemistry of the coastal water, and that, in turn, is recorded in the accretionary growth banding of the shell. By analyzing shells of scallops collected in different areas, the researchers hope to get a year-by-year picture of temperature changes in different parts of Antarctica over the past century.